Mechanisms underlying enhanced infection prophylaxis for advanced HIV in Africa

Around one-quarter of people with HIV in Africa have very advanced disease when they start treatment, and one-in-ten die during the first few months of taking HIV medicines. Deaths occur due to a variety of different infections and from a failing immune system, which is over-active but not efficient at fighting infections (so-called 'immune activation'). In the REALITY clinical trial, which enrolled 1805 children and adults in four African countries, we showed that giving these patients a 'bundle' of 5 different types of anti-infection medicines during the first 3 months of HIV treatment led to a 27% reduction in deaths. This new approach could save 3 lives for every 100 people treated with these extra anti-infection medicines, and has the advantage of being easy to deliver at community-based health clinics in Africa. Before scaling up this new intervention to reach more people with advanced HIV, decision-makers (such as the World Health Organization and National Ministries of Health) need to understand the pros and cons of such an approach. To help inform this process, we now need to understand exactly how this bundle of anti-infection medicines works.

In the REALITY study, the 'bundle' reduced tuberculosis and fungal infections, but did not seem to have an effect on the number of worm or bacterial infections that were reported during the study. It is possible, therefore, that we do not need to include the 2 antibiotics (albendazole and azithromycin) that were meant to prevent worm and bacterial infections. If these two medicines are not needed in the 'bundle' this would save costs and reduce the risks of both side effects and developing antibiotic resistance. On the other hand, we may have missed diagnosing bacterial and worm infections in patients who died, because there are few facilities that can test for these infections in Africa and some patients died at home. This study will use blood and stool samples collected from patients who died or survived in the REALITY trial to try and understand how the bundle of anti-infection medicines worked. We will look at using more sensitive methods for detecting these bacteria and worms (by identifying their genetic material in patient samples) to see if azithromycin and albendazole helped to prevent infections in the bloodstream or gut. We will also look to see if these anti-infection medicines helped to reduce the high levels of unhealthy immune activation, which may stop people dying by preventing the immune system from getting exhausted and failing completely.

If we find evidence that albendazole and azithromycin are important in reducing deaths, then they clearly need to be included in the bundle of anti-infection medicines. If we find no evidence that they contributed to reducing deaths, then they could be removed from the 'bundle'. Finally, even with this new bundle of care, 11% of patients with advanced HIV died by the end of the first year of HIV treatment, and we clearly need new ways of reducing this high ongoing death rate. It is possible that the 5 anti-infection medicines and the way in which we chose to give them were not enough, and that other approaches to preventing infections, reducing immune activation and improving the health of the gut are needed. The laboratory studies we plan to do will help to understand the reasons people still die, and what the next intervention trial might be to help avoid this.

Mortality is high in HIV-infected patients starting antiretroviral therapy with advanced disease in sub-Saharan Africa. The REALITY trial, which enrolled 1805 adults and children with CD4<100 cells/uL in Kenya, Uganda, Malawi and Zimbabwe, showed that enhanced prophylaxis (cotrimoxazole plus 12 weeks isoniazid and fluconazole, 5 days azithromycin and single-dose albendazole) reduced 24-week mortality by 27% compared to cotrimoxazole. We now need to understand how this bundle works, whether all components are required and whether additional interventions could reduce mortality further.

Enhanced prophylaxis reduced TB and cryptococcal disease but not severe bacterial infections. Our first question is therefore whether azithromycin and albendazole are needed in the bundle, or should be refined in a scaled-up intervention. Our second question is to ascertain how enhanced prophylaxis works at the mechanistic level. Understanding this would help to delineate which underlying pathogenic pathways are most tractable to intervention, and inform future approaches.

We will use a case-cohort design to evaluate the contribution of subclinical infections, enteropathy and immune activation to mortality in 602 participants and to assess whether the randomised interventions perturb these processes. Using plasma, PBMCs and stool collected at baseline, 4 and 12 weeks, we will evaluate i) subclinical bacteraemia and microbial translocation by qPCR and broad-range 16s rDNA PCR with next-generation sequencing; ii) enteropathy using a range of biomarkers to evaluate bacterial and helminth carriage, enterocyte damage, intestinal inflammation, epithelial regeneration, gut barrier function and microbial translocation; and iii) multiplex soluble inflammatory markers and T-cell immunophenotyping by flow cytometry. We will estimate associations between each marker and mortality using Cox regression models, random effects models and principal components analysis.

Adults and children living with HIV will be the key beneficiaries of this work, by refining the bundle of enhanced prophylaxis that will be taken to scale to reduce mortality. REALITY showed that enhanced prophylaxis has the potential to save one life for every 3.3 individuals treated. The aim of the current proposal is to understand whether all components of this anti-infection bundle are required, by evaluating the pathways underlying mortality through detailed laboratory studies. If we find that bacterial and helminth infections do drive mortality and are reduced by enhanced prophylaxis, then including all components in the bundle is critical; if we find no evidence that azithromycin and albendazole contribute to mortality reduction, then the bundle of care can be simplified, which would reduce costs, and reduce the potential risk of toxicity and antimicrobial resistance. This substudy will include samples from adults and children, ensuring that findings are equally relevant to scale-up of this intervention for the 1.7 million children living with HIV.

REALITY trial participants provided specimens and data to answer the questions in this proposal and we have ensured regular engagement of participants throughout the trial at each site. We will continue to work with participants and community representatives to ensure that findings from the current study are fed back to patients through workshops and discussions.

National and international policymakers will be engaged through briefings and blogs, and by presentation of data to the World Health Organization, which is planning additional focused guidance on management of advanced HIV in the near future. Co-applicants on this proposal (Prendergast, Gibb, Bwakura) are current or former members of the WHO guideline development group for HIV and have experience in translating research into policy. WHO uses the GRADE approach to evaluate evidence, so findings from this substudy will help to understand risks, benefits, feasibility and resource use associated with this bundle of care if it is to be delivered at scale.

UK taxpayers, who will ultimately fund this work, will be engaged through public lectures and interactive school visits run by the Centre of the Cell at QMUL (www.centreofthecell.org) - a unique, state-of-the-art science education centre housed within a working biomedical institute.

Scientists in sub-Saharan Africa will benefit from further development of basic science research capacity including the capacity to perform (and develop) an expanded repertoire of novel assays that may be applicable in many other research settings not just advanced HIV. We will provide the opportunity for one African researcher to gain a Masters or PhD (Uganda, Malawi or Kenya) and one junior faculty member to receive advanced training and mentorship (Zimbabwe) through this study and through immunology masterclasses with generic skills training.